O3S, the Open System Simulation Solution, simulates the whole environment of a given system for testing, debugging and IV&V purposes, with Model In the Loop (MIL), Software In the Loop (SIL), and Hardware In the Loop (HIL) capabilities. The system is jointly developed by OpenTekhnia and Techniware and uses POCO and Applied Informatics' OSP, Remoting and DNSSD toolkits.